| This thesis describes the construction and characterization of a new terrestrial laser scanning instrument built for the purpose of recording and retrieving the 3-D structure of forest vegetation. The Dual-Wavelength Echidna RTM Lidar (DWEL) uses the differential reflectances of vegetation targets at two IR wavelengths (1 mum and 1.5 mum) to characterize forest structure by distinguishing between leaves and trunks at an angular resolution as fine as 1 mrad. The DWEL instrument records the full waveforms of return signals from 5-ns laser pulses at half-nanosecond time resolution, provides single-target range resolution of 4.8 cm and 2.3 cm for the 1-pm and 1.5-mum channels, respectively, separates adjacent pulse returns in the same waveform at a distance of 52.0 cm and 63.8 cm apart for the 1-mum and 1.5-mum channels, respectively, and obtains +/-117° zenith and 360° azimuth coverage out to a radius of more than 70 meters. The angular resolution is in part controlled by user-selectable divergence optics and is shown to be < 2 mrad for the standard resolution mode, while the signal to noise ratio is 10 in both channels at 70-meter range for targets with leaf-like reflectance. The portability and target retrieval capabilities make the instrument an ideal ground-based lidar suited for vegetation sensing. |
